Process for fluid coking and coke gasification in an integrated system

ABSTRACT

A method is provided for fluid coking and coke gasification in an integrated system. High temperature gases with entrained solids are delivered to a heating zone from the gasifier without the use of a cyclone, and mixed with either circulating coke from the reactor zone in a preferred embodiment, or with circulating coke from the heater zone in an alternative embodiment. The relatively cooler gaseous heater zone effluent is treated to separate gases and entrained solids.

United States Patent [1 1 [111 3,779,900

Molstedt Dec. 18, 1973 [54] PROCESS FOR FLUID COKING AND COKE 3,694,3469/1972 Blaser et a]. 208/]27 GASIFICATION IN AN INTEGRATED SYSTEMPrimary Examiner-Herbert Levine [75] Inventor: Byron V. Molstedt, BatonRouge, Chasm, 6t

[73] Assignee: Esso Research and Engineering Company, Linden, [57]ABSTRACT [22] Filed: Nov. 30, 1971 [211 App]. No: 205,775 A method isprovided for fluid coking and coke gasification in an integrated system.High temperature gases with entrained solids are delivered to a heatingzone CI 43/197 from the gasifier without the use of a cyclone, and

2 /3 201/38, 201/44 mixed with either circulating coke from the reactor[51] Int. Cl C10g 9/32 one in a preferred embodiment, or withcirculating [58] Field of Search...., 208/127 coke from the heater zonein an alternative embodiment. The relatively cooler gaseous heater zoneefflu- [56] References Cited cm is treated to separate gases andentrained solids.

UNITED STATES PATENTS 2,734,853 2/l956 Smith et al .i 208/127 6 Claims,2 Drawing Figures VAPOR mapucrs scar/seek HEHTER IPMENIEUBEB 1 8 1913 8.779,8UU

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PRODUCTS PROCESS FOR FLUID COKING AND COKE GASIFICATION IN AN INTEGRATEDSYSTEM This invention relates to a process for fluid coking and cokegasification in an integrated system.

Large quantities of residuum remain after distilling out naphtha,heating oil, and heavy gas oil from the crude. Residuurn by itself isworth far less than the crude and must be treated or upgraded in somemanner which is economically attractive. Fluid coking has provided anefficient, lowcost process to convert residuum into more valuable lightproducts.

It has previously been found to be desirable to provide a burner orgasifier zone operated at temperatures of between l,800 to 2,000 F.where coke and/or combustible gases are burned to supply heat requiredto sustain the coking reaction. The systems of U. S. Pat. No. 2,880,167to C. N. Kimberlin, Jr. et al., and commonly owned copending U. S.application Ser. No. 17,802 filed Mar. 9, 1970, now U. S. Pat. No.3,702,5 l 6, by E. C. Luckenbach are exemplary of systems employing suchhigh temperature units. The products of such a high temperature zone aregases with entrained fine solids. Such prior art systems required theuse of a high temperature cyclone to remove the entrained solids.However, high temperature cyclones are extremely costly because,although a satisfactory cyclone design for operation at 2,000 F. hasbeen devised and demonstrated, the scale up to commercial size is notentirely predictable. Accordingly, it would be desirable to avoid theuse of the high temperature gasifler cyclone.

A previous attempt to eliminate the cyclone, placed the heater unitdirectly above the gasifler in a completely integrated unit. The top ofthe gasifier was opened to permit the hot gases to rise directly throughthe bottom of the heater unit. This system, although near ideal intheory, was far less than ideal in practice because of the critical andcomplex integrating arrangement required. The gases from the gasifierplus other gases such as air or steam which were introduced into theheater were required to fluidize a bed of coke in the heater directlyabove the open bottom thereof. And, any fluctuation in gasifieroperation would greatly affect the performance of the heater. Thus,costly, difficulty-designed equipment is required to approach desirableoperation: l) the top of the gasifler must be necked down by a criticalamount, which must be critically related to (2) a conical bottom of theheater section, which must be critically related to (3) a properlydesigned disc and donut redistributor for passing the gases through anegg crate or other suitable type grid which supports the solids in theheater bed. These internals must be cooled by recirculation of solidsfrom the heater bed through the egg crate baffle. Design and operabilityare quite problematical, largely as they relate to interactions betweenthe two beds in terms such as the control of bed levels, control ofsolids recirculation to prevent excessive temperatures on the internals,etc.

The only previously known way to eliminate these problems was tocompletely separate the gasifler from the heater and operate themindependently. However, two major disadvantages result; namely, l)substantially higher cost, mainly due to the need for high temperaturecyclones on the gasifler, which also entail serious design andmaintenance problems, and (2) loss to vide an improved process for fluidcoking which avoids the use of a high temperature cyclone at thegasifler zone.

It is a further object of this invention to provide an improved processfor fluid coking which avoids the use of a high temperature cyclone atthe gasifler zone while avoiding the disadvantages attendant to a fullyintegrated system but retaining the principal advantages thereof.

These and other objects are achieved by providing an improved processfor fluid coking in a system having a coking reactor zone which operateswithin the temperature range of 900 to l,200 F., a heating zone whichoperates within the temperature range of l,000 to l,400 F., and agasifler zone which operates within a temperature range of 1,300 to2,500 F. comprising: admixing the hot gases including entrained solidsissuing from the gasifler, with a relatively cooler stream of cokeparticles, whereby the coke particles are heated and the hot gases arecooled, conducting the resultant admixture into the heating zone; andexiting the gases from the heating zone along with any gases produced inthe heating zone through a solids-gas separating zone wherein solidparticles are recovered for re-use in the coker reactor. This inventionthus provides a way of separating solids from a hot gasifler streamwithout the need of a gas-solids separator operating at high gasifiertemperatures.

The present invention will become more apparent from the ensuingdiscussion with reference to the drawings wherein:

FIG. 1 is a flow diagram illustrating a preferred embodiment of thisinvention wherein hot gases plus any entrained solids are passed fromthe gasifier zone and mixed with relatively cooler coke from the cokingreactor before passing the combined stream into the heater; and,

FIG. 2 is a flow diagram illustrating an alternative embodiment of thisinvention wherein hot gases plus any entrained solids from the gasifierzone are joined with a stream of relatively cooler coke particles fromthe heater zone before passing the combined stream into the heater zone.

The drawings are intended only to provide an understanding of theinventive features of this invention and are not intended to becomprehensive or limiting. Much detail as to conventional systems andequipment has been omitted to simplify the explanation. Like parts aredesignated by like numerals in all the various FIGS.

Referring now to FIG. 1, a carbonaceous material having a Conradsoncarbon of at least 15 percent, such as heavy residuum boiling at l,050F.+, or a coal char slurry, or tar sands oil is passed by line 2 intothe top of scrubber 4 where it flows downwardly countercurrent tovaporous reaction products and collects in the bottom from where it ispassed by line 6 to the upper portion of coking zone 8 onto a fluidizedbed of solid particles, e.g., coke of 40 to 1,000 microns in size,maintained at a temperature of 900 to l,200 F. and preferably 950 to1,050 F. The reactor zone is maintained at a pressure of 5-50 psig., andpreferably 7-30 psig. The contact of the heavy hydrocarbons in the feedand hot solid particulate material results in the heavy hydrocarbonsbeing converted to coke and light hydrocarbons and gases which areremoved overhead through cyclone 10 and exit line 12 into scrubber 4where they are scrubbed by incoming feed. Steam, or other substantiallyinert fluidizing gas, is injected into the base of the vessel by line 14and serves to fluidize the solids therein and also strips the solids inthe lower portion of the reactor before they are removed therefrom vialine 16.

Very significant additional heating value is potentially available fromthe cracked products to be derived from the circulating coke streamentering the heater from the coking reactor. Some hydrocarbon vapors arenot stripped away from the coke in passing through the stripper and arethereby passed into the heater system. In addition, there is an amountof heavy residual hydrocarbon material left on the coke issuing from thecoking reactor. This material is subject to further cracking at thehigher temperatures prevailing in the heater system. The main productsof these two hydrocarbon sources are hydrogen, plus methane, and smalleramounts of other light hydrocarbons. In typical prior systems, thesewould become burned with air in the heater bed. However, with theembodiment shown in FIG. 1, the coke plus the entrained hydrocarbons arepassed from the coking reactor 8 via line 16 and into line 18 where theyare heated in the absence of oxygen by the high temperature productgases from the gasifier 20. Simultaneously, with the heating of the cokewhich would cause further cracking and release of entrainedhydrocarbons, the hot product gases from the gasifier are cooled. Thecombined stream is then passed via line 18 into the heater 22 above ornear the top of the heater bed, thus insuring full recovery of crackedproducts for inclusion into the total fuel gas being produced andeliminating the need for a high temperature cyclone to remove entrainedsolids from the gasifier product gases.

The product gases of the gasifier are produced by passing steam plus airor oxygen via line 23 to fluidize the bed of coke covered solidparticles which are passed from heater 22 via line 24 to the gasifier20. The bed temperature in the gasifier is maintained at a temperatureof between l,300 to 2,500 F. and preferably 1,500 to 2,000 F. Thepressure in the gasifier is maintained at between to 50 psig andpreferably between to 35 psig.

A bed of coke covered solid particles is maintained in the heater at atemperature of between about 1,000 and l,400 F. and preferably between1,l00 to 1,200 F. The pressure in the heater is maintained at about 5 to50 psig and preferably from about 7 to 30 psig. Air or oxygen is fedinto heater 22 via line 26 to fluidize the bed and to cause oxidation ofthe coke to heat the solid particles of the bed in heater 22. A portionof the solid particles in the heater bed is transferred via line 28 tocoking reactor 8 in amounts sufficient to supply the necessary heat forthe endothermic coking reaction. The product gases from the heater andthose from the gasifier which have been transferred to the heater vialine 18 and cooled by mixture with the coke from line 16 are removedthrough cyclones (not shown) and exit line 30. Solid coke particles fallback into the fluidized bed of heater 22. Although the gases exitingline 30 contain a large percentage of relatively inert combustion gases,they still have a relatively high heating value and may be used forvarious purposes as is, or the more valuable hydrocarbons may be removedtherefrom by procedures known to the art. Ash and any excess cokeproduced over that used may be purged from the system and the gasifiervia line 32.

The method illustrated by the embodiment of FIG. 1 is preferred becauseit most nearly approaches full utilization of all hydrocarbon gasproducts. Also, the embodiment of FIG. 1 recovers more of the heat fromthe high temperature gasifier product gases than does the embodiment ofFIG. 2. This is true, because coke from the reactor via line 16 iscooler than recirculated coke from the heater via line 24. Thus themixture in line 18 is somewhat cooler in the FIG. 1 embodiment than itis in the case of FIG. 2. The alternative embodiment of FIG. 2 isessentially that as shown in FIG. 1 except that the coke from the cokingreactor is passed by line 16 to the heater 22. A portion of the coke isthen withdrawn from the heater bed via line 34 which passes it into line18 where it is admixed with the hot gases from the gasifier 20. Thiscombined stream is then passed by line 18 into heater 22 at or above thetop of the bed. Passing this combined stream to the top of the bed asindicated, instead of passing it into the bed through the bottom of theheater, avoids preferential burning of any valuable hydrocarbon gaseswhich may be present by the air or oxygen which is supplied to theheater via line 26.

While the method of this invention provides for a well integrated systemfor efficient fluid coking, it also provides for a high degree offlexibility in operation. In either of the embodiments illustrated byFIGS. 1 and 2, the fluid coking system can be operated with almostcomplete independence of the gasifier. In fact, as an extreme example,the gasifier can be shut down and the coker can function in normalfashion. By the same token, variability in the gasifier operation has aminor influence on the control and performance of the fluid cokingsystem.

In a specific example of this invention, carrying out the methodillustrated by the embodiment of FIG. 1, 12,000 B/SD of l,050 F.+residuum having a Conradson carbon value of 21.8 weight percent is fedinto a coking reactor containing a bed of fluidized coke particlesmaintained at a temperature of 975 F. The reactor is operated at apressure of 20 psig. Steam is passed into the bottom of the reactor andstripper at a total rate of 555 pound moles per hour. The heater isoperated at a temperature of 1,150 F. and a pressure of 19 psig. Air ispassed into the bottom of the heater at a rate of 1,630 pound moles perhour. Coke is removed from heater 22 at a rate of 2,260 pounds perminute and is passed by line 24 to gasifier 20 which is maintained at atemperature of 1,800 F. and operated at a pressure of 22 psig. The cokein the gasifier bed is fluidized and partially oxidized by passing steamat a rate of 4,000 pounds per hour and air at a rate of 6,030 poundmoles per hour through the bottom of the gasifier. Product gases exitthe gasifier via line 18 at a rate of 8,100 pound moles per hour andcarry with them entrained coke at a rate of 1,670 pounds per minute.This stream of hot gases and entrained coke is combined with coke fromthe coking reactor which is passed by line 16 into line 18 at a rate of32,000 pounds per minute. This combined stream is then passed by line 18to the top of the heater bed. The total product fuel gas from the heateris then separated from entrained solids by cyclones and is passed fromthe heater via line 30. The results calculated for heating value in BTUsper hour of these heater product gasesand is shown below in Table I.

TABLE I Gasification Products only 300 million Cracked Hydrocarbons from269 million Circulating Coke Total 569 million Thus, it can be seen, aspreviously described, that the heater product gases produced inaccordance with this invention, especially the embodiment illustrated byFIG. 11, have a very high heating value due in great measure to theavoidance of preferential burning of the cracked hydrocarbons andgasifier product gas via the air or oxygen introduced into the bottom ofthe heater. Table II below shows the losses that may be sustained ifvarious intermediate percentages of the cracked products are allowed tobe burned in the heater in a system which does not employ the method ofthe embodiment illustrated in FIG. 1.

TABLE II Approximate 7 Heating Value Loss In BTU/SCF Gas Heating Value,Total Gas Including All Cracked Hydrocarbons I50 Total Gas WhenHydrocarbons Are Burned ln Heater I. If 50% are burned I 24 2. If 75%are burned 97 35 3. If 100% are burned 79 47 Although, the method of theembodiment shown in FIG. 2 does not have the full sensible heat recoveryadvantage discussed above for the system of FIG. 1, it does avoid thepreferential burning of the gasifier fuel gas which would occur if itwere injected, along with air, into the bottom of the heater. Thus, italso recovers full fuel value of the combined gasifier product gas andcracked hydrocarbons.

While the process has been described with respect to the circulation ofcoke as the fluidized medium, it is to be understood that a captive bedof fluidized inert particles such as silica, alumina, zirconia,magnesia, alundum or mullite, or combinations thereof may be used. Theymay also be particles built up of vanadium, nickel, or othercontaminants in the feed. The materials may be synthetically prepared ormay be naturally occurring materials such as pumice, clay, kieselguhr,diatomaceous earth, bauxite and the like. This can be advantageous forsystems in which substantial quantities of very fine (less than about 10microns) particles of foreign solids are released in the gasifier suchthat very low velocities would be required in order to maintain a stablefluidized bed. Such a captive bed can be fluidized readily withoutsignificant entrainment of the captive bed particles at superficialvelocities substantially higher than the entrainment velocity of fineparticles released from the coke. A captive bed of this type provides awell mixed reaction zone in the gasifier in which the carbon can beburned and the foreign solids released without causing severefluidization problems. Some equilibrium concentration of the fineparticles is retained in the gasifier bed, thus providing sufficientresidence time for complete gasification of the carbon before the bulkof the particles are entrained by the exit gases. This type of processwould be preferable when processing feeds containing much higher solidsthan are normally present in petroleum residua, e.g., bitumen from coal,tar sands or shale which may contain 15-20 percent inert solids. Thesolids, such as fine sand, metal oxides, or the like, contained in thebitumen are released in the captive bed in the gasifier and, beingsmaller than coke, are more easily entrained out and carried upwardlythrough the heat exchange bed. Entrainment will also be high if theresiduum fed to the unit has an unusually high Conradson carbon content,resulting in high coke yield.

The particle size should be adjusted to balance surface area requiredfor good coking with high vessel velocities. A particularly desirabledistribution of particle sizes is one in which the mix containsrelatively dense small diameter particles and less dense large particlesas described in Ser. No. 782,377 filed Dec. 9, 1968 by E. C. Luckenbach.The average particle size should be maintained between about 60 andmicrons. Considerable fines will be entrained in the gasifier gasespassed to heater 22 by line 18 due to the elimination of the cyclone atthe gasifier zone. It has been found to be desirable to circulate themback to the coker reactor, from the heater zone, where the very finestwould agglomerate on coarser particles and the rest would act as seedcoke in maintaining particle size.

It will be obvious to those skilled in the art that variousmodifications and changes can be made without departing from the spiritand scope of the present invention, an outstanding feature of which isthe cooling of the hot gasifier gases by a relatively cooler stream ofcoke particles which eleminates the need for a high temperature cycloneat the gasifier zone and increases the yield of usable product gases.

What is claimed is:

1. In an integrated fluid coking-gasification process, wherein fluidizedparticles circulate through a system comprising a coking zone containinga fluidized bed of solid particles maintained at a temperature of about900-l,200 F., and a heating zone containing a fluid bed of solidparticles maintained at a temperature of about l,000-l ,400 F a steamgasification zone containing a fluid bed of solid particles maintainedat a temperature between about l,3002,500 F. to produce a gaseouseffluent comprising hydrogen and carbon monoxide, the improvement whichcomprises combining the hot total gaseous effluent of said gasificationzone including entrained solids with a relatively colder stream of cokedsolid particles, in the absence of oxygen, to preheat said coked solidparticles and correspondingly cool said gasification effluent by heatexchange, passing the resulting combined stream into said heating zoneabove the fluid bed to heat said coked solid particles, removing atleast a portion of the heating zone gaseous effluent containingentrained solids through a solids-gas separating zone and recovering afuel gas comprising hydrogen and carbon monoxide from said separatingzone.

2. The process of claim 1, wherein said relatively cold stream of cokedsolids particles comprises coked solid particles withdrawn from saidcoking zone.

' 3. The process of claim 1, wherein said relatively cold stream ofcoked solid particles comprises coked solid particles withdrawn fromsaid heating zone.

4. The process of claim 1, wherein said gasification zone temperature ismaintained between l,500-2,000 F.

5. The process of claim 4, wherein said coking zone temperature rangesfrom about 950-l ,050 F. and said heating zone temperature from aboutl,lOO1,200 F.

6. In an integrated fluid coking-gasification process, wherein fluidizedparticles circulate through a system ranges comprising a coking zonecontaining a fluidized bed of solid particles maintained at atemperature of about 900l,200 F., a heating zone containing a fluid bedof solid particles maintained at a temperature of about l,O00-l,400 F.,a steam gasification zone containing a fluid bed of solid particlesmaintained at a temperature between l,300-2,500 F. to produce a gaseouseffluent comprising hydrogen and carbon monoxide, the

ingzone.

2. The process of claim 1, wherein said relatively cold stream of cokedsolids particles comprises coked solid particles withdrawn from saidcoking zone.
 3. The process of claim 1, wherein said relatively coldstream of coked solid particles comprises coked solid particleswithdrawn from said heating zone.
 4. The process of claim 1, whereinsaid gasification zone temperature is maintained between 1,500*-2,000*F.
 5. The process of claim 4, wherein said coking zone temperatureranges from about 950*-1,050* F. and said heating zone temperatureranges from about 1,100-1,200* F.
 6. In an integrated fluidcoking-gasification process, wherein fluidized particles circulatethrough a system comprising a coking zone containing a fluidized bed ofsolid particles maintained at a temperature of about 900*-1,200* F., aheating zone containing a fluid bed of solid particles maintained at atemperature of about 1,000*-1,400* F., a steam gasification zonecontaining a fluid bed of solid particles maintained at a temperaturebetween 1,300-2,500* F. to produce a gaseous effluent comprisinghydrogen and carbon monoxide, the improvement which comprises combiningthe hot total gaseous effluent of the gasification zone, includingentrained solids, with a relatively colder stream of coked solidparticles withdrawn from said heating zone, in the absence of oxygen,passing the resulting combined stream into said heating zone above thefluid bed, removing at least a portion of the heating zone gaseouseffluent containing entrained solids through a solids-gas separatingzone and recovering a fuel gas comprising hydrogen and carbon monoxidefrom said separating zone.